[#640] Implement consistent fuzz packet naming

The convention is that all packets used in fuzzing have the file extension
.pkt.  This commit has renamed some packets to match that convention.

diff --git a/src/bin/dhcp6/tests/fuzz-data/release-fqdn b/src/bin/dhcp6/tests/fuzz-data/release-fqdn.pkt
similarity index 100%
rename from src/bin/dhcp6/tests/fuzz-data/release-fqdn
rename to src/bin/dhcp6/tests/fuzz-data/release-fqdn.pkt

diff --git a/src/bin/dhcp6/tests/fuzz-data/renew-fqdn b/src/bin/dhcp6/tests/fuzz-data/renew-fqdn.pkt
similarity index 100%
rename from src/bin/dhcp6/tests/fuzz-data/renew-fqdn
rename to src/bin/dhcp6/tests/fuzz-data/renew-fqdn.pkt

diff --git a/src/bin/dhcp6/tests/fuzz-data/request-simple b/src/bin/dhcp6/tests/fuzz-data/request-simple.pkt
similarity index 100%
rename from src/bin/dhcp6/tests/fuzz-data/request-simple
rename to src/bin/dhcp6/tests/fuzz-data/request-simple.pkt

diff --git a/src/bin/dhcp6/tests/fuzz-data/solicit-docsis-relayed b/src/bin/dhcp6/tests/fuzz-data/solicit-docsis-relayed.pkt
similarity index 100%
rename from src/bin/dhcp6/tests/fuzz-data/solicit-docsis-relayed
rename to src/bin/dhcp6/tests/fuzz-data/solicit-docsis-relayed.pkt

diff --git a/src/bin/dhcp6/tests/fuzz-data/solicit-fqdn b/src/bin/dhcp6/tests/fuzz-data/solicit-fqdn.pkt
similarity index 100%
rename from src/bin/dhcp6/tests/fuzz-data/solicit-fqdn
rename to src/bin/dhcp6/tests/fuzz-data/solicit-fqdn.pkt

diff --git a/src/bin/dhcp6/tests/fuzz-data/solicit-simple b/src/bin/dhcp6/tests/fuzz-data/solicit-simple.pkt
similarity index 100%
rename from src/bin/dhcp6/tests/fuzz-data/solicit-simple
rename to src/bin/dhcp6/tests/fuzz-data/solicit-simple.pkt